The present invention relates to wound drain catheters for draining fluid from, or supplying medication to, a closed deep wound. This invention also relates to a method for attaching a stainless steel trocar to a silicone outflow tube of a catheter.
Virtually all wound drain catheters used in closed wounds comprise a drain portion for fluid communication with the wound and an outflow or extension tube portion. Typically, the tube portion is connected to a vacuum supply after (a) the drain has been placed in the wound and (b) the wound, or surgical incision, has been closed. The most common type of prior art drain comprises a length of tubing which is perforated by forming spaced apertures through the tubing wall. These apertures are usually in opposed pairs and, while the spacing between aperture pairs may vary, such aperture pairs are typically spaced by a distance equal to approximately twice the diameter of the tubing. One major problem with these prior art drains is that wound debris, such as clots, may block a number of the apertures, thereby substantially reducing the effectiveness of the drain. A more serious problem is that, as the wound heals, tissue tends to grow into the apertures. Such tissue growth not only blocks the apertures, but, in addition, when the physician removes the drain by applying a strong pulling force on the catheter, the portion of tissue that has grown into the apertures will be literally ripped from the patient's body. This causes severe discomfort to the patient and retards the healing process. Moreover, if the tissue growth into the aperture is extensive, the drain may break when the physician attempts to remove it, thereby leaving a portion of the drain in the patient's body. If this occurs, additional surgery may be required to extract the broken portion of the drain.
A further disadvantage of prior art perforated drains is that their apertures tend to structurally weaken the drain. Since the cross-sectional area of the drain body is reduced at each of the apertures, the apertures create weak points in the drain tube wall. Further, when tensile forces are applied to the drain, the tensile stresses at the top and bottom of an aperture are particularly high, since the tensile forces are unable to pass across the aperture. That is, the material adjoining the aperture must carry the stresses which are unable to bridge the aperture in addition to its normal share of the stress. Thus, an area of discontinuity, such as an aperture, is commonly referred to as a "stress raiser". Perforated drains, therefore, are much weaker than their drain body cross-sectional area suggests, since each of the perforations creates a "stress raiser".
Moreover, since perforated drains have a tubular structure, they tend to kink when bent or squeezed, as by movement of the patent. If this occurs, the effectiveness of the drain may be substantially impaired, thereby warranting premature removal of the drain.
Wound drains made from a silicone elastomer are usually preferable to drains made from other materials, since silicone is highly biocompatible, soft, and flexible. In contrast, materials such as PVC are more rigid, and therefore, tend to irritate the wound. This causes substantial discomfort to the patient and inhibits healing. Further, PVC is less biocompatible than silicone. Materials such as natural rubber are seldom ued for closed wound drains because of toxicity problems. Thus, silicone is typically the most advantageous material for closed wound drains. However, silicone is not as strong as PVC, and thus, it tends to rupture more easily during drain removal from a closed, deep wound. This has limited the usefulness of silicone drains in many applications.
For the purpose of illustrating the structural characteristics of a typical perforated drain, one exemplary form of prior art perforated drain, in common and widespread use, will be described. This exemplary drain has an outside diameter D, an inside diameter about one-half D, opposed pairs of perforations having a diameter of about one-half D, and an axial spacing of about 2D. Using well known mathematical formulas, it may be found that this exemplary drain has a lumenal drainage area of 0.196D.sup.2, a tissue contact drainage area of 0.196D.sup.2 units per unit D of length, and a drain body cross-sectional area of 0.0307D.sup.2 at each of the aperture pairs. These parameter values will be subsequently compared to corresponding parameter values for the present invention, in order to contrast the significant improvements in drain effectiveness and strength provided by the present invention.
Non-perforated drains have been proposed for use in shallow surface wounds, such as those created by plastic surgery. For example, a drain of this type is illustrated in U.S. Pat. No. 3,860,008, issued to Miner et al. Another similar type of non-perforated drain is disclosed in U.S. Pat. No. 105,038 (British), issued to Liddell. Both of these drains, however, are specifically designed to be patent to the atmosphere, rather than to an outflow tube. Thus, the drain is always exposed to infection causing organisms. Consequently, the problems associated with closed, deep wounds, such as providing an aseptic environment, and providing safe, reliable drain removal while maintaining drain effectiveness, are not addressed.
Several techniques may be used to insert a wound drain catheter in the patient's body. For example, a surgeon may simply place the drain portion and a small part of the outflow tube portion in the wound, close the incision, and suture around the outflow tube portion. This technique is somewhat unsatisfactory, since it is difficult to completely seal the area around the outflow tube by suturing, and thus, the wound may become infected. A more satisfactory technique is to pass a trocar, preattached to the end of the outflow tube, through healthy tissue by entering the patient's body at a point within the wound and exiting at a point adjacent to the wound. The surgeon pulls the outflow tube portion through the tissue with the trocar until the catheter is properly positioned, with the drain in the wound. Since the outflow tube exits the body at a point adjacent the wound, the wound can be completely closed by suturing, thereby reducing the risk of infection.
When outflow tubes made from silicone are used, the trocar and the tube sometimes separate, leaving the end of the outflow tube in the patient's body. If this occurs, the outflow tube must be removed and the procedure repeated. Such separation is due to the difficulty of attaching the trocar to the outflow tube. Typically, the end of the trocar includes a connector portion having annular ridges which grippingly engage the inner surface of the outflow tube. However, since a silicone catheter tube is soft and flexible, it tends to easily detach itself from the annular ridges when subjected to tensile force. Accordingly, there is a need for an improved method of attaching a silicone catheter tube to a trocar.